1. Technical Field
The present invention relates to protective helmets and in particular to an improved helmet retention system which provides a secure and consistent fit of such helmets for a wide variety of head shapes and sizes.
2. Background Information
Protective headgear is widely used in military applications not only to provide protection against impact hazards, but also to safeguard the wearer against the effects of excessive noise. It is well known that the protection conferred by a properly fitted helmet is superior to that obtainable from a loosely fitting one. In recent years this requirement for secure fitting has assumed even greater importance, since the protective helmet in many of its applications has acquired a secondary role as an integral part of sophisticated weapons systems. Such systems involve the addition to the helmet of head-mounted sighting/designation equipment which inevitably causes a shift in the helmet's center of gravity. This in turn leads to an increased tendency for the helmet to move in relation to the wearer's head. Any movement of this kind is regarded as undesirable lest it cause a loss of bore sight, i.e., a loss of alignment between the optical axis of the sighting system (on the aircraft) and the optical axis of the display system (on the helmet). It is vital that helmet-mounted equipment should fit onto the wearer's head in the same precise location each time the helmet is donned. Equally, the helmet must not slip as a result of the changing gravitational forces encountered during flight or when traversing bumpy terrain.
The fitting of a helmet which includes a sighting/designation system can take a skilled technician many hours and even more time can be spent during a refit if use of the helmet is contemplated in combination with a chemical protective respirator. It is probable that military operations in remote locations will limit the availability of such technicians, thereby making the initial fit and any subsequent refit of the helmet very difficult.
The majority of helmet fitting systems are based on the use of either webbing strap and pad combinations, or else filler materials are used such as polyurethane foam to center the head of the wearer in the helmet shell. In some systems thermoplastic filler materials are used which are molded to the head shape of an individual wearer. Unfortunately, this centering operation can result in an increase in separation between the wearer's eyes and the image display such that the wearer's field of view through the sighting/designation system is reduced.
By contrast, the fitting system of the present invention works by urging the wearer's head forward so that it is pushed firmly against the brow piece inside the helmet. Preferably, the ear cups are simultaneously urged inwards to firmly engage the sides of the wearer's head in order to minimize side-to-side movement of the helmet. The first of these two operations is essential to ensure that the wearer's eyes are positioned as far forward as possible and fall within the exit pupil of the sighting/designation equipment, and also to ensure that the wearer's head is returned to the same relative position each time the helmet is donned. This consistency in positioning of the head is the key to obtaining greatest possible accuracy from helmet-mounted sighting/designation equipment.
Circumstances may also arise in which it is necessary for non-military personnel to wear a protective helmet in order to perform a specific task, for example when airlifting emergency medical personnel by helicopter to the scene of an accident. In these circumstances it is unlikely that the personnel called upon will possess their own helmets, yet it is desirable that they should be equipped with helmets having a good fit. It is equally unlikely that the helicopter reserve equipment will include a variety of helmets in different sizes, since these would not only take up a great deal of space but would also contribute unnecessary weight to the aircraft.
It is an object of this invention to alleviate some of the drawbacks of known helmets by providing a helmet having an improved retention and fitting system which gives a reliable and stable fit without requiring intervention by skilled technicians and which can be adjusted for varying conditions without compromising the protective capabilities of the helmet or the accuracy of its sighting/designation equipment if such is fitted. It is also an object of this invention to provide a helmet having a retention and fitting system which can be adjusted by a non-expert to variations in wearers' head dimensions so that a single helmet can be worn by a variety of users on different occasions.